Energy collection and power reduction in laser coupling process

ABSTRACT

An energy collector is used to assist a laser coupling process by reducing the amount of output power of a laser that is used to modify a device attaching element. The energy collector includes an energy collector tip configured to be placed proximate to a device attaching element during the laser coupling process. The energy collector tip is configured to receive laser energy reflected from the device attaching element during the laser coupling process and is formed from a material that converts this reflected energy to heat. Sufficient thermal coupling is created between the energy collector and a surface to provide a conductive pathway for the energy, which has been converted to heat, between the energy collector and the device attaching element.

FIELD OF THE INVENTION

The present invention relates generally to an apparatus for assisting ina laser coupling process by reducing the required amount of laser power,and, in particular, to an apparatus for collecting laser energyreflected from a device attaching element and converting the laserenergy to heat during the laser coupling and fiber attach process.

BACKGROUND OF THE INVENTION

Laser soldering for attaching multiple components may be used in avariety of systems, including optical systems, electronic systems andmicro-mechanical systems, including micro-electro-mechanical systems(MEMS) and micro-opto-electro-mechanical systems (MOEMS). For example,laser soldering may be used to securely position an optical fiber tocouple the optical output from a laser diode into the optical fiberduring the construction of laser transmitters. Typically, fiber-coupleddiode lasers are packaged in metal butterfly packages, which may be goldplated. The fiber is held in alignment with the laser using a deviceattaching element such as epoxy, a laser weld, or a solder attachmentwith or without a ferrule. Epoxy attachment is low cost but may have toomuch thermal expansion for high precision attachments. Furthermore, itmay not be reliable over a long period of time due to outgassing andalignment shifts arising from aging and temperature cycling. Laser weldtechniques are reliable but use costly ferrulization of the fiber andspecially designed mounts or clips to allow weld attachment of theferrulized fiber. The mounts and clips tend to be relatively large, andmay creep over time.

Solder attachment techniques, which have become prevalent in the art,may be more reliable and less costly. Laser soldering techniques alsoreduce the chance of static discharge that may potentially damage thecomponents. Laser soldering techniques however, require relatively highamounts of laser power. A significant amount of the laser's power may belost or wasted due to the highly reflective nature of the soldersurface. The large amount of power used by the laser in a typical lasercoupling process makes such a process relatively expensive compared, forexample, with an epoxy coupling process. This cost may be reduced bysupplying an additional low cost energy source near the solder such asan inductive heating source, a direct heater or a thermo-electric cooler(TEC). These low cost energy sources however, do not enable specifictarget soldering within a small space without affecting the surroundingarea. The additional equipment may also add complexity to the system.Further, the additional equipment may be expensive.

SUMMARY OF THE INVENTION

To reduce the amount of laser power required during the laser couplingprocess, it may be desirable to use the lost or wasted energy reflectedby the solder preform to help heat the solder preform. For thisreduction in laser power, a simple, inexpensive apparatus is needed.

The present invention is embodied in an exemplary energy collector usedto assist a laser coupling process. The energy collector includes anenergy collector tip that is placed at a location near a deviceattaching element during the process so that the collector tip receiveslaser energy reflected from the device attaching element. The energycollector tip is formed from a material that converts the reflectedlaser energy to heat.

The present invention is also embodied in a system used in a lasercoupling process. The system includes a laser and an energy collectorcoupled to the laser. The energy collector includes an energy collectortip that is placed at a location near a device attaching element duringthe laser coupling process so that the collector tip receives laserenergy reflected from the device attaching element. The energy collectortip is formed from a material that converts the reflected laser energyto heat.

The present invention is also embodied in a method for reducing theamount of power used by a laser for coupling a plurality of components.The exemplary method includes placing a device attaching element on asurface and placing an energy collector proximate to the deviceattaching element. The energy from a laser beam that is reflected off ofthe device attaching element is collected by the energy collector. Themethod creates sufficient coupling between the energy collector and thesurface to provide a thermally conductive pathway for the energy betweenthe energy collector and the device attaching element. The method thenuses the collected energy of the laser beam to assist in modifying thedevice attaching element.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawing. It is emphasizedthat, according to common practice, the various features of the drawingare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawing are the following figures:

FIG. 1A is a is a side plan drawing illustrating an exemplary energycollector, including an area of physical contact between the exemplaryenergy collector and a surface that provides sufficient thermal couplingaccording to one embodiment of the invention.

FIG. 1B is a side plan drawing illustrating another exemplary energycollector, including a smaller area of physical contact between theexemplary energy collector and a surface that provides sufficientthermal coupling according to one embodiment of the invention.

FIG. 1C is a side plan drawing illustrating another exemplary energycollector that is placed near a surface with no physical contact betweenthe exemplary energy collector and the surface that provides sufficientthermal coupling according to one embodiment of the invention.

FIG. 2 is a front plan drawing of an exemplary solder preform with aporous surface that may be used during a laser coupling processaccording to one embodiment of the invention.

FIG. 3 is a side plan drawing illustrating another exemplary energycollector that partially surrounds a device attaching element andincludes an opening for a laser beam to pass through and irradiate thedevice attaching element according to one embodiment of the invention.

FIG. 4 is a side plan drawing illustrating another exemplary energycollector that is placed on a surface that includes a thermallyconductive coating according to one embodiment of the invention.

FIG. 5 is a side plan drawing illustrating another exemplary energycollector that is coupled to a top surface of an attachment padaccording to one embodiment of the invention.

FIG. 6 is a flowchart illustrating an exemplary method for collectingenergy reflected from a device attaching element and using the collectedenergy to assist in modifying the device attaching element according toone embodiment of the present invention.

FIG. 7 is a cut-away side plan drawing illustrating an exemplary energycollector, cut along a center line of the exemplary energy collector andincluding a channel to provide a pathway for gas to flow.

FIG. 8 is a side plan drawing illustrating an exemplary system thatincludes a laser, an energy collector and a controller coupled togetheraccording to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1A shows an exemplary embodiment of the invention. As shown, laserbeam 104 irradiates device attaching element 106 which is located onsurface 102. Laser energy 108 is reflected from device attaching element106 in different directions. Energy collector tip 100 is proximate todevice attaching element 106 so that at least a portion of the laserenergy 108 is collected by energy collector tip 100. Energy collectortip 100 is also in contact with surface 102. The precise location ofenergy collector tip 100 and the area of collector tip 100 that is incontact with surface 102 shown in FIG. 1 is merely illustrative and isnot limiting.

It is contemplated that the device attaching element may be made of anumber of different materials used during a laser coupling process,which have the desired thermal and mechanical properties. It is notedthat the desired thermal and mechanical properties may vary depending onthe type of components which are being coupled. These materials mayinclude solder, thermally cured epoxy, ultraviolet (UV) cured epoxy, andair-cured epoxy. Exemplary solder preforms may desirably be formed ofany solder alloy which has the desired thermal and mechanicalproperties, such as glass solder, lead-tin solder, gold-based solder,indium-based solder, gallium-based solder, bismuth-based solder,cadmium-based solder, or lead-free solder, wherein the solder preformmay be with or without flux.

It is contemplated that the energy collector tip may be made of a numberof different materials which have desired thermal and mechanicalproperties. It is noted that the desired thermal and mechanicalproperties may vary depending on the type of components used during thelaser coupling process. Desirably, an energy collector tip is made up ofmaterials with thermal conductivity sufficient to heat an area proximateto the device attaching element to a predetermined temperature less than100 ms after the laser beam begins to irradiate the device attachingelement and sufficient to cool the area proximate to the deviceattaching element to a predetermined temperature less than 100 ms afterthe laser beam stops irradiating the device attaching element. Exemplaryenergy collector tips may desirably be formed of any material which hasthe desired thermal and mechanical properties, such as iron, steel orceramic.

Referring to FIG. 2, it may be desirable to use a solder preform that isless reflective to further reduce the amount of laser power requiredduring the laser coupling process. FIG. 2 illustrates an exemplarysolder preform with a porous surface. As shown in FIG. 2, solder preform200 is formed from multiple smaller solder chips 202. Desirably, solderchips 202 have diameters in the sub-micron range. Solder chips 202 forma more porous surface on solder preform 200. While laser energy 206 fromlaser beam 204 is reflected from solder preform 200, laser energy 208 isabsorbed by solder preform 200 which helps to heat the solder preform. Aporous solder preform may be made by placing solder chips 202 into ametal die cast.

FIG. 6 is a flow chart diagram illustrating an exemplary method forcollecting energy reflected from a device attaching element and usingthe collected energy to assist in modifying the device attachingelement. At step 600, a device attaching element is placed on a surface.Next, the user places an energy collector tip proximate to the deviceattaching element at step 602. The exact location of the energycollector tip may be determined from various factors. For example, asdescribed below, the location may be determined by energy collector tipmaterial. The exact location of the energy collector tip may also bedetermined by the amount of laser energy reflected from the deviceattaching element that the user desires to collect with the energycollector tip. The user may place the energy collector tip at a locationsuch as shown in FIG. 1A. Alternatively, the user may desire to placethe energy collector tip closer to the device attaching element tocollect more laser energy reflected from the device attaching element asshown, for example, in FIG. 3.

Laser energy is collected from a laser beam that is reflected from adevice attaching element, at step 604. The amount of energy collectedmay be determined by the location of the energy collector tip asdescribed above. The amount of energy collected may also be determinedby the material that forms the energy collector tip. As described above,it is contemplated that the energy collector tip may be made of a numberof different materials which have desired thermal and mechanicalproperties that may vary depending on the type of components used duringthe laser coupling process.

At step 606, sufficient thermal coupling is created between the energycollector and the surface to provide a conductive pathway for the energybetween the energy collector and the device attaching element.Sufficient thermal contact may be determined from various factors,including the material that makes up the energy collector, the materialthat makes up the surface, the power of the laser and the amount of timeused to heat and cool the area proximate to the device attaching elementas described above. For example, an energy collector with a greater areaof physical contact will conduct heat through the surface to the deviceattaching element in a shorter amount of time than one with a smallercontact area. The user may determine that physical contact between theenergy collector and the surface may be desirable for sufficient thermalcoupling as shown, for example, in FIG. 1A. FIG. 1B illustrates anotherexemplary embodiment of the invention. As shown, the area of energycollector tip 120 is also in physical contact with surface 122. The areaof physical contact shown in FIG. 1B however, is smaller than the areaof physical contact shown in FIG. 1A. A mechanism may be used to applyforce to the energy collector tip to ensure good physical contactbetween the energy collector tip and the surface. The mechanism forapplying the force to create the area of physical contact may include aspring which biases the energy collector tip toward the surface. It iscontemplated however, that other methods for applying the force may beused.

FIG. 3 illustrates another exemplary embodiment of the invention. Asshown in FIG. 3, energy collector tip 300 is placed on surface 302 andpartially surrounds device attaching element 306. Energy collector tip300 includes opening 310 enabling laser beam 304 to pass through andirradiate device attaching element 306. Laser energy 308 is reflectedfrom device attaching element 306 and collected by energy collector tip300. Because it completely surrounds the device attaching element 306,the exemplary embodiment shown in FIG. 3, may collect a greater amountof energy than the exemplary embodiments shown in FIG. 1A, FIG. 1B andFIG. 1C.

FIG. 1C illustrates another exemplary embodiment of the invention. Asshown in FIG. 1C, energy collector tip 130 is not in physical contactwith surface 132. The user may determine that energy collector tip 130however, is placed at a distance from surface 132 so that there issufficient thermal coupling, for example via radiational coupling,between energy collector tip 130 and surface 132.

Thermal coupling may also be increased by placing a thermally conductivecoating on the surface and/or on the surface of the energy collector.FIG. 4 illustrates another exemplary embodiment of the invention, whichincludes energy collector 400 and device attaching element 406 placed onan area of thermally conductive coating 404. Thermally conductivecoating 404 may also be a factor for determining sufficient thermalcontact. For example, the user may desire a smaller area of physicalcontact between the energy collector tip and the surface or may desireto place an energy collector tip near the surface if there is athermally conductive coating because the thermally conductive coatingmay conduct heat through the surface to the device attaching element ina shorter amount of time.

FIG. 5 illustrates another exemplary embodiment of the invention, whichincludes an attachment pad 502. Energy collector 500 is placed on a topsurface 504 of attachment pad 502. Device attaching element 506 is alsoplaced on attachment pad 502. A thermally conductive coating (not shown)may also be placed on attachment pad 502.

Referring back to FIG. 6, at step 608, the collected energy is used toassist in modifying the device attaching element. As described above,the energy collector tip may be made of materials having thermalconductivity sufficient to heat an area proximate to the deviceattaching element to a predetermined temperature less than 100 ms afterthe laser beam begins to irradiate the device attaching element andsufficient to cool the area proximate to the device attaching element toa predetermined temperature less than 100 ms after the laser beam stopsirradiating the device attaching element. Although it is contemplatedthat the collector tip may be made up of materials with differentthermal properties, at least one property convert the laser energyreflected from the device attaching element to heat. Although the energycollector tip is described as converting energy reflected from thedevice attaching element to heat, it is contemplated that it may alsoconvert energy directly applied to the collector tip to heat.

After the laser energy is converted to heat energy (heat), the heat maybe used to help modify the device attaching element during the lasercoupling process. As described above, sufficient thermal coupling iscreated between the energy collector and the surface to provide aconductive pathway for the heat to travel between the energy collectorand the device attaching element so as to heat the surface near thedevice attaching element. Therefore, the laser energy collected by theenergy collector is used to help in the modification process which mayresult in a more homogeneous heating of the device attaching element.

Referring to FIG. 7, it may be desirable to provide a gas to an areanear the device attaching element to assist in the process for heatingthe device attaching element more homogeneously. The gas that isprovided to the area near the device attaching element may be heated byheat at the surface or heat from the device attaching element. The gashowever, may be heated more homogeneously than the surface or the deviceattaching element which has become heated from the energy collected bythe energy collector and the laser energy absorbed by the deviceattaching element. Therefore, the gas may assist in heating the deviceattaching element more homogeneously during the laser coupling process.FIG. 7 is a cut-away side plan drawing illustrating an exemplary energycollector, cut along a center line of the exemplary energy collector andincluding a channel to provide a pathway for gas to flow. As shown inFIG. 7, energy collector 700 is placed on surface 702 and includeschannel 704 which provides a pathway for gas to flow from energycollector 700 to an area proximate to device attaching element 706 toassist in modifying the device attaching element. Exemplary sources ofgas may use inert gases that do not chemically react with thesurrounding elements such as the energy collector, surface material orthe device attaching element. Exemplary gases may be, for example,nitrogen, argon, or carbon-monoxide.

It may be desirable to heat the gas before it reaches the area proximateto the device attaching element. The gas may be heated before it entersthe channel in the energy collector. Alternatively, or in addition thegas may be heated by the heat from the energy collector as it passesthrough the channel. It is also contemplated that the gas may be appliedto the area proximate to the device attaching element without using achannel in the energy collector. A gas which is not sent through achannel may be heated prior to reaching the area near the deviceattaching element. After the collected energy has been used to assist inthe modification of the device attaching element, the process end atstep 610.

It may also be desirable to provide a gas to assist in the coolingprocess. The gas may be cooled to a predetermined temperature to enhancethis process. The gas may be provided to the area proximate to thedevice attaching element without using a channel in the energy collectortip. Alternatively, the gas may be provided to an area proximate to theenergy collector through the channel.

Various methods may be used to apply the heat used in the laser couplingprocess. For example, the user may modify a device attaching element bylaser pulse heating. This exemplary method may provide very precisecontrol of the location and volume of the device attaching element beingmodified. At least one pulse of laser light from a pulsed laser source,such as a pulsed direct diode laser may be used to irradiate themodified device attaching element. A number of parameters may be usedfor determining laser types, ranges of power, pulse widths andwavelengths such as the material of the device attaching elements, thematerial of the energy collector, the proximity of the energy collectorto the device attaching element and the efficiency of the couplingprocess being used, but in any case it is desirable for the pulses oflaser light incident on the device attaching element to have a fluencethat is less than the ablation threshold of the material of the deviceattaching element. It has been found that a direct diode laser with alaser beam having an output power in the range of about 20 W to 40 W,wavelengths in the range of about 800 nm to about 1000 nm and pulsewidths in the range of about 100 ms to about 1 s, perform well formodifying device attaching elements formed of a fluxless glass solder.

Referring to FIG. 8, it may be desirable to use a system during thelaser coupling process where the laser and the energy collector arecoupled together. As shown in FIG. 8, energy collector 800 is placed onsurface 802 and proximate to device attaching element 804 to collectlaser energy 808 reflected from device attaching element 804. Energycollector 800, laser 810 and controller 812 are coupled together.Controller 812 may be configured to control the movement of energycollector 800, the movement of laser 810 and/or the pulse width andoutput power of laser beam 806. Controller 812 may configured to controllaser 810 and energy collector 800 so that they are rigidly coupled andthe movements of laser 810 and energy collector 800 are dependent oneach other. It may also be desirable for controller 812 to be configuredso that laser 810 and energy collector 800 move independently of eachother. For example, the energy collector 800 may be moved to be alignedwith device attaching element 804 at a desired location for collectinglaser energy 808 reflected from device attaching element 804.Alternatively, laser 810 may be moved after energy collector 800 hasbeen aligned with device attaching element 804 to collect laser energy808 reflected from device attaching element 804.

It may be desirable to keep the energy collector stationary and move thedevice attaching element to align the device attaching element with theenergy collector. The device attaching element may be on the surface ofa substrate or an attachment pad and the movement of the deviceattaching element may include moving the substrate or the attachment padto align the device attaching element with the energy collector. Acontroller may be configured to move the device attaching element alongan x-y plane or in three dimensions so that the device attaching elementis aligned with the energy collector.

An energy collector tip holder may also be coupled to an energycollector tip. The energy collector tip holder may include a mechanismfor applying force to the energy collector tip to create sufficientthermal coupling between the energy collector tip and the surface, asdescribed above. The energy collector tip holder may also be used tocouple the energy collector to a controller. As described above, anenergy collector tip is desirably made up of materials with thermalconductivity sufficient to heat an area proximate to the deviceattaching element to a predetermined temperature less than 100 ms afterthe laser beam begins to irradiate the device attaching element andsufficient to cool the area proximate to the device attaching element toa predetermined temperature less than 100 ms after the laser beam stopsirradiating the device attaching element. It is noted however, that thedesired thermal properties may vary depending on the type of componentsused during the laser coupling process. Therefore, exemplary energycollector tip holders may be made of a number of different materialswhich have the desired thermal properties. For example, the energycollector tip holder could be made up of materials with a greaterconductivity than the energy collector tip to assist in the coolingprocess. Alternatively, the energy collector tip holder could be made upof materials with less conductivity which acts as an insulator andassists in the heating process.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

1. An energy collector used to assist a laser coupling process, theenergy collector comprising: an energy collector tip configured to beplaced proximate to a device attaching element during the laser couplingprocess, wherein: the energy collector tip is configured to receivelaser energy reflected from the device attaching element during thelaser coupling process; and the energy collector tip is formed from amaterial that converts the laser energy reflected from the deviceattaching element to heat.
 2. An energy collector according to claim 1,further including a mechanism for applying force to the energy collectortip to create thermal contact between the energy collector tip and asurface and to provide a thermally conductive pathway for the collectedenergy between the energy collector tip and the device attachingelement.
 3. An energy collector according to claim 1, further comprisingan energy collector tip holder coupled to the energy collector, whereinthe material that forms the energy collector tip holder has at least thesame thermal conductivity of the energy collector tip to assist incooling an area proximate to the device attaching element when the laserenergy is no longer applied.
 4. An energy collector according to claim1, further comprising an energy collector tip holder coupled to theenergy collector, wherein the material that forms the energy collectortip holder has a thermal conductivity less than energy collector tip toassist in heating an area proximate to the device attaching element whenthe laser energy is applied.
 5. An energy collector according to claim1, wherein the energy collector includes a channel which provides apathway for a gas to flow from the energy collector tip to an areaproximate to the device attaching element.
 6. An energy collectoraccording to claim 1, wherein the material that forms the energycollector tip has a thermal conductivity sufficient to heat an areaproximate to the device attaching element to a predetermined temperatureless than 100 ms after the laser beam begins to irradiate the deviceattaching element and sufficient to cool the area proximate to thedevice attaching element to a predetermined temperature less than 100 msafter the laser beam stops irradiating the device attaching element. 7.An energy collector according to claim 1, wherein the material thatforms the energy collector tip includes at least one of iron, steel orceramic.
 8. An energy collector according to claim 1, wherein the energycollector tip at least partially surrounds the device attaching elementand the collector tip includes an opening such that the laser beam maypass through the opening and irradiate the device attaching element. 9.A system used in a laser coupling process, the system comprising: alaser; and an energy collector coupled to the laser, the energycollector including: an energy collector tip configured to be placedproximate to a device attaching element during the laser couplingprocess, wherein: the energy collector tip is configured to receivelaser energy reflected from the device attaching element during thelaser coupling process; and the energy collector tip is formed from amaterial that converts the laser energy reflected from the deviceattaching element to heat.
 10. A system according to claim 9, the systemfurther including a mechanism for applying force to the energy collectortip to create sufficient thermal contact between the energy collectortip and a surface to provide a conductive pathway for the collectedenergy between the energy collector tip and the device attachingelement.
 11. A system according to claim 10, wherein the mechanism forapplying force to the energy collector tip includes a spring whichbiases the energy collector tip toward the surface.
 12. A systemaccording to claim 9, wherein the laser is rigidly coupled to the energycollector.
 13. A system according to claim 9, wherein the laser iscoupled to the energy collector so that the laser and energy collectormove independently of each other.
 14. A system according to claim 9,wherein at least one of the energy collector or the device attachingelement is moved to align the energy collector with the device attachingelement.
 15. A system according to claim 9, wherein the device attachingelement is formed of at least one of glass solder, lead tin solder,gold-based solder, indium-based solder, gallium-based solder,bismuth-based solder, cadmium-based solder, lead-free solder, thermallycured epoxy, air-cured epoxy or ultraviolet cured epoxy.
 16. A systemaccording to claim 9, wherein the device attaching element is formed ofa solder preform including a plurality of sub-micron solder chips.
 17. Asystem according to claim 9, wherein the laser beam has a wavelength inthe range of about 800 nm to about 1000 nm.
 18. A system according toclaim 9, wherein the laser beam has a power in the range of about 20 Wto 40 W.
 19. A system according to claim 9, wherein the laser beam has apulse length in the range of about 100 ms to about 1 s.
 20. A systemaccording to claim 9, wherein the surface at which sufficient thermalcontact is created is a top surface of an attachment pad and the deviceattaching element is located on the top surface of the attachment pad.21. A system according to claim 9, wherein the surface includes athermally conductive coating.
 22. A system according to claim 9, whereinthe energy collector includes a channel that provides a pathway for agas to flow from the energy collector tip to an area proximate to thedevice attaching element.
 23. A system according to claim 22, the systemfurther including a source of gas coupled to the channel.
 24. A systemaccording to claim 22, wherein the gas is selected from a groupconsisting of nitrogen, argon, or carbon-dioxide.
 25. A method forreducing the amount of power used by a laser for coupling a plurality ofcomponents, the method comprising the steps of: placing a deviceattaching element on a surface; placing an energy collector proximate tothe device attaching element; collecting energy from a laser beam thatis reflected from the device attaching element; creating sufficientthermal coupling between the energy collector and the surface to providea conductive pathway for the energy collected by the energy collector toflow to the device attaching element; whereby the collected energy isused to assist in modifying the device attaching element.
 26. A methodaccording to claim 25, the method further comprising the step ofinjecting a gas through a channel in the energy collector to an areaproximate to the device attaching element to assist in modifying thedevice attaching element.
 27. A method according to claim 26, whereinthe step of injecting a gas through a channel in the energy collectorfurther includes injecting heated gas through the channel.
 28. A methodaccording to claim 27, wherein the step of injecting heated gas throughthe channel further includes using the energy collected by the energycollector to heat the gas as it passes through the channel.
 29. A methodaccording to claim 25, wherein the step of creating sufficient thermalcoupling between the energy collector and the surface includes applyingforce to the energy collector to create sufficient thermal contactbetween the energy collector and the surface.
 30. A method according toclaim 29, wherein applying force to the energy collector to createsufficient thermal contact includes using a spring which biases theenergy collector toward the surface.